This is an application for an ADAMHA Research Scientist Award. The research proposed covers two broad areas: the ontogeny and complex usage of vocal signals by monkeys and the reproductive physiology and breeding behavior of the same animals. The research on vocal communication involves descriptive studies of vocal development in normally-reared and rejected and hand- reared pygmy marmosets and cotton-top tamarins. Both the ontogeny of vocal structure and the ontogeny of appropriate usage of calls will be studied. Of particular interest is a 'babbling' phase where infants produce long strings of calls that seem to be practicing for adult structure. The role of social suppression of hormonal activity and the release from these hormones will be studied, and the complex integration of vocal duetting will be examined during the early stages of pairing of two animals. Studies involving intersubstitution of individual notes within complex calls will be attempted to study the importance of syntax in adult vocal sequences. The studies of hormonal function will make use of our non-invasive technique for gathering urine samples from individual marmosets and tamarins while living in normal social groups, and our ability to analyze the major gonadal steroids as well as luteinizing hormone/chorionic gonadotropin. Five different studies will be done. First, we will do a comparative survey of hormonal functioning across the reproductive cycle of ovulation, conception, pregnancy, parturition and lactation for 6 species representing 4 of the 5 genera of the family Callitrichidae. These animals have striking differences on mechanisms of reproductive suppression and in gestational length which have not been well-examined. Second, we will develop a urinary prolactin assay and use it to determine the role played by prolactin in the reproductive suppression found in cotton-top tamarin males and females, and in the paternal care displayed by male tamarins. Third, we will pursue our findings that olfactory stimuli from the mother are responsible for maintaining ovarian suppression and that stimulation by a male is needed to organize ovarian cycles. These studies will involve using familiar and unfamiliar males and testing different components of maternal secretions. Fourth, we will develop precise odor discrimination techniques to evaluate whether male tamarins can detect ovulation or early pregnancy in their mates. Finally, we will continue our longitudinal studies of aging tamarins to determine if anything equivalent to menopause appears.